...There is a quick and easy method for doing this using the keyboard: close and relaunch InDesign, and IMMEDIATELY hold down Ctrl + Alt + Shift (Windows) or Cmd + Ctrl + Opt + Shift (Mac), and respond in the affirmative to the dialog asking if you really want to replace the preferences. There are two downsides to this method, however. First, you must be extremely fast on the keyboard (if you don’t see the confirmation prompt, you were too slow), and second, anytime you replace the preferences you will lose most program customizations, and using the keyboard method leaves you with no backup to restore them when the problem turns out to be something else...